Laundry dryer.
EPO Patent 0512940-A1

The clogging of the lint filter of a tumbler dryer with lint and fluff from the laundry being dried causes a reduction of the air transport exceeding that caused by the filling with laundry. This necessitates more frequent regulation of the input temperature (27) to the drum of the tumbler dryer than if the lint filter were clean or totally removed. It is therefore possible to measure the frequency of regulation and compare it to a value obtained by experience gained by drying operations with a clean lint filter. If the frequency of regulation is too high an alarm is triggered, indicating the requirement for cleaning the lint filter.